1. Field of the Invention
The present invention relates to a fiber optic module and a method for making the module.
2. Background Information
Fiber optic cables have been developed as a medium to transfer information within a communication system. The fibers are linked to optical transmitters and optical receivers. The transmitters typically include electronic circuits that drive a light source such as a laser diode. The laser diode emits a modulated light beam that travels through the fiber optic cable to a photodetector.
It is critical to accurately align the fiber cable with the laser diode to minimize optical power losses. There have been developed numerous fiber optic modules that package the laser diode and fiber cable in a manner to align the cable to the diode. By way of example, U.S. Pat. No. 5,619,609 issued to Pan et al. and assigned to E-Tek Dynamics, Inc., discloses a fiber optic module which includes a clip that is used to align the fiber optic cable with a laser diode. The clip is mounted to a substrate and laser welded to a ferrule of the fiber optic cable. The clip has an oversized channel which allows the fiber optic cable to be vertically adjusted relative to the laser diode.
In accordance with the teachings of the Pan reference the fiber optic cable is assembled into the module by initially placing the cable within the package adjacent to a laser diode. The laser diode is excited to direct a light beam through the fiber optic cable. The other end of the optic cable is coupled to a receiver unit which can determine the amount of optical power transmitted through the fiber.
The position of the fiber is varied until a predetermined optical power is detected by the receiver unit which corresponds to an optimal alignment position of the cable. The fiber is then removed from the package and the clip is placed on a package substrate. The fiber cable is re-inserted into the module and onto the clip at the optimal position. The cable is adjusted until a maximum optical power is detected to indicate alignment between the cable and the laser diode. The clip is then laser welded to the substrate. The fiber optic cable is once again adjusted until the cable is aligned with the diode. The ferrule of the cable is then laser welded to four corners of the clip.
It is desirable to minimize the amount of time required to align the fiber optic cable to the laser diode. Each second of assembly time increases the cost of mass producing the module. It would be desirable to reduce the time required to align the fiber optic cable with the laser diode. It would also be desirable to provide a clip that is conducive to a more efficient, automated, repeatable method for aligning the fiber cable with the laser diode.
The adjustment of the fiber during the alignment process is typically performed by an operator who manually moves the fiber. The adjustment of the fiber can occur both before and after a laser weld. Manually adjusting the fiber requires a certain level of skill and patience. It would be desirable to fully automate the adjustment process to minimize the skill and time required to align the fiber with the diode.
As discussed in the Pan reference the laser welding process creates local heating and shrinkage which can shift the position of the ferrule. The power and paths of the laser beams used to laser weld the ferrule to the clip can be adjusted to fine tune the position of the fiber optic cable. U.S. Pat. No. 4,747,657 issued to Chaoui et al. discloses a process for fine adjustment and alignment of a fiber optic cable subassembly with an optical device subassembly utilizing the shrinkage and shifting of the parts during the laser welding process. Such a technique is sometimes referred to as laser hammering.
In Chaoui the subassemblies are initially laser welded together at two opposite points of adjoining mating surfaces. Light is transmitted through the fiber and detected during the alignment process. An additional laser weld is then created adjacent to one of the initial weld locations. The shrinkage created by the additional weld spot will further shift the fiber cable toward the direction of the spot. Light transmitted through the fiber cable is then detected to determine whether there was an increase or decrease in light intensity. If the light intensity increased an additional weld spot is created adjacent to the two previous weld locations. If the light intensity decreases a weld spot is created adjacent to the other initial weld location. This iterative process continues until the fiber is aligned with the laser diode. As discussed in the Chaoui reference thirty-six weld spots may be required to align the fiber optic cable with the laser diode. This process may be time consuming and ultimately increase the cost of mass producing fiber modules. It would be desirable to provide an automated method to quickly align a fiber optic cable with a laser diode within a fiber module. It would also be desirable to predict and characterize any weld shifts and minimize the number of welds required to align the filter with the light.